The piezoelectric component is for example a piezoelectric actuator with a monolithic actuator body. The actuator body for example comprises a number of piezoelements arranged one on top of the other. A single piezoelement has at least two electrode layers arranged one on top of the other in a stacking direction and at least one piezoelectric layer containing the piezoceramic element (piezoceramic layer) arranged between the electrode layers. The piezoelements are arranged such that electrode layers and piezoelectric layers are arranged in an alternating manner one on top of the other. Each of the electrode layers, referred to as internal electrodes, functions as the electrode layer of adjacent piezoelements. For the purposes of electric contact with the electrode layers, adjacent electrode layers are guided in an alternating manner to two lateral surface sections of the actuator body, which are insulated electrically from each other. The actuator body has strips of metallic coating on each of these surface sections.
A piezoelectrically active region of the piezoceramic layer is located between the electrode layers of the respective piezoelement. Electrical activation of the electrodes causes a relatively homogeneous electric field to be induced in this region of the piezoceramic layer. Homogeneous deflection of the piezoceramic layer results over the entire piezoelectrically active region. In contrast every piezoceramic layer is piezoelectrically inactive in the region of the described surface sections. The alternating guiding of the electrode layers to the surface sections causes an electric field to be injected into the piezoelectrically inactive region of the piezoceramic layer, which is significantly different from the electric field injected into the piezoelectrically active region of the piezoceramic layer. During electrical activation of the electrode layers, in other words during polarization and/or during operation of the piezoactuator, the different electric (polarization) fields cause different deflections of the piezoceramic layer in the piezoelectrically active region and in the piezoelectrically inactive region. As a result mechanical stresses occur in the piezoelement, which can lead to what is known as a poling fissure at right angles to the stacking direction. This poling fissure can continue into the metallic coating attached to the surface sections of the actuator body. This causes a break in the electric contact of at least some of the electrode layers of the actuator body.
To reduce the probability of poling fissures occurring during polarization of a monolithic actuator body, a specific polarization method is specified in DE 197 56 182 C2 for the piezoactuator described above. The actuator body comprises several hundred piezoceramic layers and electrode layers arranged in an alternating manner. The piezoceramic layers are made of a lead zirconate titanate (PZT). The electrode layers are made of a silver-palladium alloy. To produce the actuator body, ceramic green films are printed with a silver-palladium paste, stacked one on top of the other, separated from the binder and sintered in a common manner.
According to the polarization method, during the application of a polarization field a mechanical compressive stress is applied at the actuator body, counteracting the elongating effect of the polarization field. This reduces the degree of the change in expansion of the piezoceramic layer in the piezoelectrically active region. A lower level of mechanical stress results in the actuator body. The probability of the occurrence of poling fissures in the actuator body is thus reduced by the method described.
The poling of the actuator body is however only one of a number of work steps required to obtain a piezoactuator that is suitable for corresponding applications. One application of the piezoactuator is for example the activation of an injection valve in an engine in a motor vehicle. The further work steps are carried out before or after polarization. For example electrical connector elements are attached to the metallic coating strips. The actuator body is generally also sealed with a plastic compound. This protects the surface of the actuator body against mechanical destruction or against electrical arcing between adjacent electrode layers. Furthermore the actuator body is not only poled under a mechanical compressive stress, it is also operated under a mechanical compressive stress. This means that the actuator body is pretensioned. To this end the actuator body (sealed with a plastic compound) is for example welded into a Bourdon spring.
At the end of the production chain described above, it must be verified whether the piezoactuator can be used in the required manner. The quality of the piezoactuator must be determined. The quality relates in particular to piezoelectric parameters of the piezoactuator, for example its d33 coefficients. It often turns out that the piezoactuator produced has piezoelectric parameters that exclude the use of the piezoactuator. Such an exclusion is frequently due to defects that occur due to sintering.